本篇研究的目的是探討豆薯在可造成寒害和非寒害的溫度下，豆薯的外觀改變、寒害病徵、品質變化、相關酵素的活性以及寒害與乙烯的相關性。將豆薯塊根貯藏在6°C寒害的環境及20°C非寒害的環境下30天，在寒害的環境下誘導豆薯塊根寒害徵狀，包括外表腐壞、內部褐化、亮度及硬度下降、總酚類化合物含量減少。低溫貯藏會誘導細胞膜的破壞，使離子滲漏率(%)、丙二醛和過氧化氫含量增加，貯藏期間寒害嚴重的豆薯塊根苯丙氨酸氨裂解酶、多酚氧化酶和過氧化酶活性有顯著增加。貯藏在6°C 9天後移至較高溫的環境下3天(15°C、20°C、25°C )，豆薯塊根的寒害症狀如外表腐壞及內部褐化更加明顯，其與膜離子滲漏、丙二醛含量、苯丙氨酸氨裂解酶及多酚氧化酶活性的增加，以及總酚類化合物的降低具相關性。結果顯示移至高溫的豆薯塊根寒害症狀嚴重，而持續在低溫貯藏可抑制乙烯生合成和呼吸率及褐化相關酵素活性，而寒害症狀不明顯。豆薯塊根在不同溫度(1°C、3°C、6°C、9°C、12°C、15°C和20°C)時呼吸率的變化，以阿瑞尼士圖顯示，呼吸率隨溫度下降而降低，並且塊根在9°C以及根圓片在7°C時斜率出現非線性情形，為塊根及組織貯藏在9°C及7°C之臨界溫度。
評估豆薯塊根在寒害下6°C貯藏12天，乙烯生成和呼吸率之變化，每隔3天將豆薯塊根移至25°C，每隔3小時測量一次，共測量24或36小時，結果顯示豆薯塊根移至高溫後，乙烯生合成和呼吸率快速上升，隨後趨向緩和。間歇性變溫處理為豆薯塊根貯藏在6°C中12.5天、每兩天移至常溫12小時後再移回6°C貯藏，間歇性變溫處理可減輕塊根及內部褐化及降低離子滲漏率(%)，在貯藏12.5天後仍維持良好外觀品質，但不能維持硬度與減輕內部褐化情形。以間歇性變溫處理塊根貯藏於6°C之乙烯生成和呼吸率顯著較低，但與塊根外表腐損、內部褐化、膜離子滲漏率的增加並不一致。1-MCP處理可以降低乙烯生成及呼吸率，但會加劇寒害症狀，如外表腐損、內部褐化、降低內部組織的明度、失重率及離子滲漏率(%)增加，顯示乙烯可能不直接影響豆薯塊根寒害症狀發生。
溫湯處理(50ºC、53ºC及55ºC)處理薯豆塊根可抑制外表腐損和內部褐化，但仍有部份寒害症狀之發生，55°C的溫湯處理不會改變豆薯塊根的硬度及亮度，同時降低離子滲漏率(%)、丙二醛及過氧化氫含量，回溫之後，但與對照組在統計上則沒有顯著差異。溫湯處理後的總酚類化合物含量仍然很高，並顯著抑制於變溫處理中常溫時的乙烯生成率，但呼吸率僅受55°C溫湯處理抑制，此處理之抗氧化能力(FRAP)亦較高，而53°C溫湯處理可顯著抑制苯丙氨酸氨裂解酶、多酚氧化酶、過氧化酶等酵素活性，但超氧化物歧化酶及過氧化氫酶的活性則不受溫湯處理之影響。結果顯示，50°C溫湯處理可維持抗壞血酸氧化相關酵素的活性。低氧處理豆薯塊根可以減輕褐化程度、維持內部組織的明度、減緩失重率，並且不影響硬度。0%低氧處理最能有效減輕褐化情形，但會增加腐損率，因過度低氧破壞了塊根的細胞膜，造成離子滲漏率(%)及腐爛率之提高。The purpose of this research was to study the characteristics changes and chilling development, quality changes and the activity of the related enzyme as well as the correlation between ethylene and the chilling damage on the jicama tuberous root during storage under chilling or non-chilling temperatures. The roots stored at 6ºC as chilling condition, and at 20ºC as non-chilling condition, for 30 days. Characteristics of chilling injury were induced by chilling condition, included external decay, internal browning, decreasing of interior tissue lightness (L*) value and total phenolic compound (TPC), and loss of root firmness. The chilling temperature induced membrane damage includes increasing of membrane ion leakage (%), malondialdehyde (MDA) and hydrogen peroxide (H2O2) content. There were significantly increased of phenylalanine ammonium-lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD) specific activities in severe symptoms of chilling injury. The increasing of external decay and internal browning were highly correlated with increasing of membrane ion leakage (%), MDA content, PAL specific activity, PPO specific activity and decreasing of TPC. For the root stored at 6ºC, 9 days after storing then transferred to higher temperature for another 3 days (15ºC, 20ºC, 25ºC or continuously at 6ºC). The severe symptoms were found in the roots which were transferred to higher temperature, whereas the ethylene production and respiration rates can reduce by low-temperature conditions. Nonlinear Arrhenius plots of respiration were found in the roots stored at various temperatures (1ºC, 3ºC, 6ºC, 9ºC, 12ºC, 15ºC, and 20ºC). The slope of the plot from root and tissue discs decreased with lower temperatures with breaks points at about 9ºC in root and at 7ºC in tissue discs.
For the evaluation of ethylene production and respiration rates, roots storing at 6ºC for 12 days. Every 3 days, roots were transferred to 25ºC for evaluation at every 3 hours for 24 or 36 hours. Ethylene production and respiration rate rapidly increased after the root were transferred to higher temperature and tended to decrease afterward. For intermittent warming treatment (IW), jicama tuberous roots were stored at 6ºC for 12.5 days. Continuously, every 2 days, roots were transferred to ambient temperature for 12 hours (after 12 hours, the roots were returned to 6ºC). Intermittent warming treatment reduced ion leakage (%), internal browning, maintained the interior tissue L* value, and showed a good appearance after storage for 12.5 days but did not maintain firmness and reduced external decay. Roots treated with IW showed significant lower in ethylene production and respiration rate than roots storing at 6ºC but these rates were not consistent with the increasing of external decay, internal browning, and membrane ion leakage (%). 1-MCP treatment reduced ethylene production and respiration but increased chilling injury symptoms, such as external decay, internal browning, decreasing of interior tissue L* value, loss of firmness, and decreasing of membrane integrity. These results indicated that ethylene probably does not directly involved in chilling injury symptom development of jicama tuberous root.
Hot water treatment (HWT, 50ºC, 53ºC, and 55ºC) suppressed external decay and internal browning development, but none of them could completely prevent all the symptoms. Firmness, lightness value, and H2O2 content were not affected by the HWT. Root treated with 55ºC hot water was lower in ion leakage percentage and malondialdehyde. Nonetheless, statistics showed that there has no significant difference as compared to control. Hot water treatment can also maintain higher level of total phenolic compound. After transferring to ambient temperature rate of ethylene production was significantly reduced by the HWT, but rate of respiration was reduced only in 55ºC HWT. PAL, PPO, and POD specific activity were significantly reduced by the 53ºC HWT. Ferric reducing ability of plasma was maintained by the 55ºC HWT. Superoxide dismutase and catalase specific activity were not affected by any treatment of the HWT. Lastly, the 50ºC HWT maintained high level of ascorbate peroxidase specific activity. Low O2 treatments can reduce browning discoloration, maintain interior tissue L* value and delay weight loss of root but did not affect the root firmness. The best browning prevention was found in root treated with 0% O2, nevertheless, high decay was also found in this treatment. Moreover, 0% O2 treatment damaged the root cell membranes, which give the rise of ion leakage (%) and decay.